The present invention relates to a control system for maintaining the operating height of the header of an agricultural combine, and for raising and lowering the header to maintain a constant operating height, as set by the operator, as the combine traverses variations in ground contour.
A system for controlling the height of the header of some currently available agricultural combines, such as the Case/New Holland 2300 Series, includes an electrical sensor coupled to a rotatable sensor shaft on which there is mounted an elongated arm referred to as a xe2x80x9csensor arm.xe2x80x9d The sensor arm of the prior art is in the form of a ground runner which engages and rides over the surface of the soil. The distance between the header and the ground is called the xe2x80x9coperating height.xe2x80x9d The operating height may change either because the operator sets a new operating height from the combine cab, or because ground contour changes as the combine moves to harvest crop. When the operating height changes due to a variation in ground contour, the sensor arm rotates the sensor shaft in one direction if the sensed operating height increases and in a counter direction if the operating height decreases. A closed-loop control system on the combine then raises or lowers the header accordingly to effect the operating height previously set by the operator. A second control system may be present on the combine, by which the lateral attitude of the header is controlled to maintain the outboard ends of the header at the same height with respect to the ground.
The present invention improves the operating performance of the prior art combine header operating height control system and lateral attitude control system (if present) described above by configuring the sensor arm so that it has an operating segment which is curved, as opposed to the prior art sensor arms which are characterized as having long straight sections. This provides a contact point with the ground (whether level or a rise or depression) which moves forward, toward a vertical plane passing through the center of sensor shaft, as the operating height decreases. The contact point moves rearward, away from the vertical plane, as the operating height increases. In other words, as the operating height decreases (e.g., a rise in the ground is encountered by the sensor), the contact point on the curved segment of the sensor arm in contact with the ground moves forward, thereby reducing the distance between the contact point and the center (or axis) of rotation of the sensor shaft. This creates a shorter lever arm for the sensor and results in a quicker response as well as a proportionately greater magnitude of response when the operating height is set at smaller values, for a given change in the ground. It is, of course, desirable to have responses which are faster and of greater magnitude when the operating height is set at smaller values because it enables the operator to traverse the ground at higher speeds without fear of running the snout of the header into the ground.
Thus, the present invention has two advantages over the prior art. First, the fore-to-aft distance between the sensor shaft and the ground contact point decreases continuously as the header is lowered (or the operating height decreases for any reason). This provides a faster system response time because the horizontal distance between the sensor shaft (and the forwardmost point of the header) and the ground contact point of the sensor arm is decreased. Thus, the sensed error occurs closer to real time and results in a reduced latency in the response time. This is a substantial operational advantage because it increases the ground speed at which the combine is able to operate with satisfactory results and without risking running the nose of the header into the ground.
Secondly, the curved contour of the ground-engaging or operating segment of the sensor arm of the present invention also shortens the distance between the axis of rotation of the sensor arm and the ground contact point of the sensor arm as the operating height decreases. The distance between the center of the sensor shaft and the ground contact point of the sensor arm is sometimes referred to as the xe2x80x9csensor lever arm.xe2x80x9d The length of the sensor lever arm determines the magnitude of the system response to a given variation in the operating height of the header. That is, the shorter the sensor lever arm, the greater is the angular displacement (i.e., rotation) of the sensor shaft for any given change in ground contour, including both increases and decreases. This feature provides a ratio-changing sensor arm in that the ratio of angular displacement of the sensor shaft increases for a given change in ground contour when the operating height is set to a lower value by the operator.
As a result, when the header is set to a lower operation height and passes over a rise in the ground, the sensor error signal is increased for a given rise in ground contour, and the magnitude of the system response is increased. The resulting operational characteristic is substantially improved, and both features (i.e., reduced response time and increased system response) are cumulative to increase the ground speed at which the combine may satisfactorily operate.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of the illustrated embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like part in the various views.